The use of cellular mobile telecommunications has undergone substantial growth over the past few years and is projected to continue expanding as service is improved and new products and features are offered. To retain existing customers and entice others to adopt cellular telecommunications, however, services must be provided at a reasonable price. Therefore, the cost of providing cellular telecommunication services must be reduced.
Conventional terrestrial-based cellular systems provide service to geographical areas divided into hexagonal cells 110 as shown in FIG. 1. The number and size of these cells are selected by the service provider such that geographical coverage is optimized, cost is reduced, and capacity within the service area is maximized. Each cell 110 is equipped with transmitters, receivers, and control apparatus located at a cell site 120, which is typically located near the geographical center of the cell. Each cell site 120 within a particular service area is connected to a central office 130 that serves as a mobile telephone switching office (MTSO) and which controls mobile operation within the cells. The cell-sites 120 connect to the MTSO over data links 125. The MTSO switches calls to other mobile units and to the local telephone system.
As a practical matter, cell boundaries are not precise. The conventional hexagonal cell shape was chosen because it provides a practical way of covering an area without the gaps and overlaps in coverage that would occur if circular cells were used. Although circular cells could be serviced by omni-directional antennas, directional antennas must be used to approximate the hexagonal shape.
Because of the above, and other, limitations of conventional terrestrial-based cellular systems, researchers have begun to design wireless communications systems that use high-altitude aeronautical platforms (HAAP) to carry radio-relay transponders. A HAAP can take, for example, the form of an airship or a piloted, or pilotless, airplane circling over a geographical service area. One advantage of an airborne antenna platform is that it can service a much larger geographical area than conventional terrestrial-based cellular antenna systems.
Attempts to realize an operational HAAP have heretofore relied on geographical service areas divided into conventional adjacent hexagonal cells. The use of conventional cells, however, requires that the HAAP on-board antenna be capable of dynamically changing its radiation pattern as the aeronautical vehicle flies in a circle above the service area. This is because the relative position between each hexagonal cell and the HAAP is not constant and, thus, the antenna beam must be mechanically and/or electronically steerable, which adds cost and complexity to a cellular system employing HAAP-mounted antennas. Thus, from the wireless point of view, the most challenging technical issue in realizing such systems is the sophisticated, steerable multi-beam antennas required onboard the HAAP.
Accordingly, what is needed in the art, is a way of clustering cells that does not require steerable-beam antennas.